Radio receiving apparatus



April 5, 1927. 1,623,918 I A. H. GREBE RADIO RECEIVING APPARATUS Filed Dec. 17. 1924 2 Sheets-Sheet l DETECTOR SOOOON HMPLI F'ER Ag, 1 W 7 A. H. GREBE RADIO RECEIVING APPARATUS April Filed Dec. 17. 1924 2 Sheets-Sheet 2 #XZZZZZT. 7km

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Patented Apr. 5, 1927.

UNITED STATES ALFRED HENRY GREBE, OF HOLLIS, NEW YORK.

RADIO RECEIVING APPARATUS.

Application filed December 17, 19%. Serial No. 756,520.

Among the defects which are inherent with the super-heterodyne type of receiver is the capability of receiving signals from a powerful local station of entirely-different wave length than that to which the receiving station has been adjusted. For the purpose of clarity of description, tuning will be referred to in terms of frequency rather than in the wave length.

In Fig. 1 is shown an arrangement in which only two of the variable elements are mechanically coupled. \Vith this exception Figs. 1 and 2 are alike and the description of the operation of the circuits holds good for both figures. The form shown in Fig. 1 is being made the subject matter of a divisional application and soeis not further discussed here.

Take for instance the case illustrated in Fig. 2 where the receiving L with its tuning condenser is adjusted to receive signals having a frequency of 1000 kilocycles when the oscillator circuit 086 is tunedto 1050 kilocycles by means of its tuning condenser C1 a beat note of kilocycles will be set up and passed on into the intermediate frequency amplifier IFA. However, if another signal having a frequency of 1100 kilocycles and of sufticient strength to set up currents in the loop pick up system L with its variable condenser G. then this undesired signal will, in conjunction withthe oscillator circuit which is tuned for 1050 kilocycles, set up the required beat note frequency of 50 kilocycles, and the latter will be passed on to the intermediate frequency amplifier IFA with the result. that both the desired and the undesired station or signal will be heard at the same time. It is the purpose of this invention to provide means for eliminating the possibility of having frequencies other than the desired one from affecting the receiving apparatus and thereby eliminate thi undesirable condition.

The variable cond users being used in this system are prefe l ably of the straight line frequency type and as such may be mechanically connected so that the adjustment may be made with one control or dial knob. Referring to the diagram, we see that variable. condenser C tunes the loop pick up system, while variable condenser C1 tunes the oscillator system. The circuits are so designed that when mechanically interlocked at the minimum pick up loopcapacity position the frequency of the oscillator circuit OSC will be 50 kilocycles higher than the frequency of the loop pick up system, which includes the condenser C. This difference will be maintained substantially constant throughout the range of the variable condensers, so that the required frequency difference will always be maintained. Referring back to the frequencies mentioned in the first part of the descrip tion, in which the loop pick up system was adjusted to 1000 kilocycles, it follows that the oscillator circuit, by reason of its variable element being mechanically connected with the variable element C, will be adjusted to 1050 kilocycles. Now, we provide a third variable circuit consisting of the inductance L1 and variable condenser C2 and couple this variable circuit to the loop pick up cir cuit by means of the coupling coil K, and arrange the constants of this circuit, which we will now call an absorbing circuit -AC, in such a manner that when the variable condenser C2 is mechanically connected with the other variable condensers C1 and C and adjust this circuit so that its frequency will always be 50 kilocycles higher than the oscillator circuits, then if powerful impulses having a frequency of 1100 kilocycles are picked u in the loop L the absorbing circuit A will absorb this unwanted frequency and the intermediate ainplifier will only respond when the frequency of the received signal corresponds with the frequency to which the loop pick up sys tem is. (or has been) adjusted.

Inasmuch as the variable elements of all three circuits are mechanically, interlocked and as these variable elements are so designed as to maintain a constant frequency difi'erenee throughout the range of their adjustments, the absorbing circuit AC will.

always be tuned to a frequency 50 kilocycles higher than the frequency of the oscillator circuit and therefore the corrective condition which was explained for he case where the loop system was adjusted for 1000 kilocycles will be maintained for all other frequency adjustments within the ran e of the variable e]eme nts.

1e foregoing description refers to the conditions in which the intermediate frequency amplifier is adjusted to operate when a frequency difference of 50 kilocycles exists between the oscillator circuit and the loop pick up circuit. This difference of 50 this naturally kilocycles has been s ecified merely for illustrative purposes. he frequency may just as readily be made higher or lower and the whole system made to function just as readily rovided the elements are designed in accor ance with a definite frequency relation and provided however that such frequency is well outside the limits of audibility. The oscillator circuit may also be adjusted to a frequency of which a harmonic is used to produce the frequency difference. In this case the absorbing circuit however will still be designed in the same manner as provided for in the first part of the description.

This system has been described in a manner which presumes the mechanical interlocking of all three variable elements and is the best way to apply the invention. However, it should be understood that all three variable elements may be made inde ndent, and of course the oscillator circult could be adjusted to a frequency either higher or lower than the loop pick up circuit and it follows that where the oscillator is tuned to a higher frequency the absorbing circuit will have to be tuned to a still higher frequency, i. e., twice the difference between the oscillator and the pick up system and on the other hand where the required intermediate frequency is produced by adjusting the oscillator to a lower frequency than the pick up circuit the absorbing circuit will have to be adjusted to a frequency still lower than the oscillator cir-- cuit, but also difl'erin from the pick up circuit by twice the difference between the pick up circuit and the oscillator circuit.

Having therefore described my invention, I claim j 1. A radio receiving system comprising means for tuning its input, adjustable means for reducin a desired signal fre uency simultaneous y with a materially di erent interfering frequency to the same lower frequency, variable means for removing the undesired frequency and means common to the three above mentioned means for varying them simultaneously.

2. In a radio receiving set utilizing the beat note method of signal reception, employing an input circuit, an osclllator circuit, and a frequency selective impedance associated with the input circuit, the method of reducing interference which consists in tuning the frequency selective impedance and the input circuit .to different frequencies,

each of these frequencies differing from that of the oscillator circuit by the same amount, and maintaining the above stated frequency relation of the two circuits and the frequency selective impedance throughout the range of the set.

3. A signal responsive system comprising an input circuit including tuning means, an oscillator circuit including tuning means, a filter circuit including tuning means, means for mechanically coupling said tuning means for simultaneous adjustment to maintain constant the difference of the input and oscillator circuit frequencies and to maintain the filter circuit so tuned as to filter out an undesired frequency Which diflers from the frequency of the oscillator circuit by an amount equal to halfthe difference between said undesired frequency and the frequency of said input circuit.

4. In a signal responsive system comprising an input circuit with tuning means, an oscillator circuit including tuning means, an absorption circuit including tuning means and an intermediate frequency amplifier, the method of eliminating interference which consists in tuning the input circuit to the desired signal frequency, tuning the oscillator circuit for a frequency differing from that of the input circuit by the frequency for which the intermediate frequency amplifier-is designed, tuning the absorption circuit for a frequency different from that of the input circuit, and differing from that of the oscillator circuit by the frequency of the intermediate frequency amplifier, and maintaining the above stated frequency relation of the three circuits throughout the range of the system.

' ALFRED HENRYGREBE. 

